Liquid-based optical device and electronic device

ABSTRACT

The present invention discloses an optical device comprising a container enclosing an insulating liquid (A) and a liquid responsive to an electric field (B), the insulating liquid (A) and the liquid responsive to an electric field (B) being immiscible and being in contact with each other via an interface ( 14 ), at least one of the liquids (A; B) being at least partially placed in a light path through the container. The optical device further comprises an electrode arrangement ( 2; 12 ) for controlling the shape of the interface ( 14 ) by means of a voltage; and means ( 100 ) for preventing the interface from an exposure to an external electric field. Consequently, the build-up of electrostatic charge on a surface of the optical device is avoided, which prevents the unwanted distortion of the interface ( 14 ) caused by the interaction of the liquid responsive to an electric field (B) and the electrostatic charge.

This is a continuation of prior application Ser. No. 10/599,865 filedOct. 12, 2006 and is incorporated by reference herein.

The present invention relates to an optical device comprising acontainer enclosing an insulating liquid and a liquid responsive to anelectric field, the insulating liquid and the liquid responsive to anelectric field being immiscible and being in contact with each other viaan interface, the liquids being placed in a light path through thecontainer; an electrode arrangement for controlling the shape of theinterface by means of a voltage.

The present invention further relates to an electronic device comprisingsuch an optical device.

Optical devices based on the manipulation of liquids are rapidly gaininglarge commercial interest, not in the least because of their lack ofmechanically moving parts and the relative simplicity of the devices,which makes the devices cheap and durable.

For instance, in US patent application US2001/0017985 an optical deviceis disclosed that incorporates two immiscible liquids with equalrefractive indices but different transmittances, with one of the twoliquids being conductive. By varying the interface between these twoliquids, the amount of each of the liquids in the light path through thedevice is changed and a diaphragm is obtained as a result.

International patent application WO03/069380 discloses a cylindricalvariable focus lens incorporating two immiscible fluids having differentrefractive indices, one of the fluids being conductive and the otherbeing insulating. The shape of the interface between the two fluids ismanipulated by applying a voltage across the lens, which can be used tointroduce a change in the focal point of the lens. The walls of thecylinder and one of the transparent lids of the cylinder are coated witha hydrophobic coating to ensure that at least in a switched off statethe conductive fluid, which typically is a polar liquid, the contactarea between said walls and the conductive fluid is minimized in orderto achieve an interface with a large curvature, which contributes to alarge optical power range for the lens.

A problem that can occur with such devices is that after a period oftime an unintended deformation of the interface can occur, whichdisturbs the desired optical behaviour of the interface.

The invention seeks to provide an optical device in which the unintendeddeformation of the interface is avoided.

The invention further seeks to provide an electronic device comprisingsuch an improved optical device.

According to an aspect of the invention, there is provided an opticaldevice comprising a container enclosing an insulating liquid and aliquid responsive to an electric field, the insulating liquid and theliquid responsive to an electric field being immiscible and being incontact with each other via an interface, at least one of the liquidsbeing at least partially placed in a light path through the container;means for controlling an orientation of the interface; and means forpreventing the interface from an exposure to an external electric field.

In the context of the present invention, the phrase ‘a liquid responsiveto an electric field’ is intended to include conductive liquids, polarliquids and polarizable liquids.

The invention is based on the realization that the unintendeddeformation of the interface is caused by its exposure to an externalelectric field, which may be a static field caused by the build-up of anelectrostatic charge on a surface of the container. The build-up of theelectrostatic charge may for instance be caused by intentional orunintentional rubbing of the surface of the container.

The means for controlling an orientation of the interface may comprisean electrode arrangement for controlling the shape of the interface bymeans of a voltage. This is especially advantageous in the case of theoptical device being a variable focus lens, because this facilitates alens with a large optical power.

In an embodiment, the surface is a part of a transparent end portion ofthe container, the means for preventing the interface from an exposureto an external electric field comprise a conductive layer, theconductive layer forming a part of the transparent end portion. This hasthe advantage that the accumulation of electrostatic charge on thetransparent end portion can be avoided.

Advantageously, the electrode arrangement comprises an electrode incontact with the liquid responsive to an electric field, the conductivelayer being conductively coupled to said electrode. In this embodiment,the conductive layer is kept at the same potential as the liquidresponsive to an electric field, thus ensuring that the presence of anyelectrostatic charge on the transparent end portion has no influence onthe shape of the interface.

In a further embodiment, the means for preventing the interface from anexposure to an external electric field comprise a Faraday cagesurrounding the container. This embodiment, which may be combined withthe previous embodiment, protects the optical device from exposure toexternal electrical fields, and consequently prohibits the build-up ofelectrostatic charge on a surface of its container.

The Faraday cage may comprise a conductive coating at least partiallycovering a further container. This has the advantage that the Faradaycage can be produced separately from the optical device.

The further container may be at least partially transparent. This hasthe advantage that the further container can completely encapsulate thecontainer of the optical device, without the optical path through thelatter being compromised.

According to a further aspect of the invention, there is provided anelectronic device including an optical device comprising a containerenclosing an insulating liquid and a liquid responsive to an electricfield, the insulating liquid and the liquid responsive to an electricfield being immiscible and being in contact with each other via aninterface, at least one of the liquids being at least partially placedin a light path through the container; means for controlling anorientation of the interface; and means for preventing the interfacefrom an exposure to an external electric field; the electronic devicefurther comprising driver circuitry coupled to the means for controllingan orientation of the interface and a power supply for powering thedriver circuitry, the means for preventing the interface from anexposure to an external electric field being coupled to a terminal ofthe power supply.

The electronic device of the present invention has the advantage thatthe performance of its optical device is not hampered by externalelectric fields such as the accumulation of electrostatic charges on asurface of the container of the optical device.

In an embodiment, the means for preventing the interface from anexposure to an external electric field are coupled to a terminal of thepower supply, preferably ground, to ensure that said means are kept on asame potential as the liquid responsive to an electric field.

In an alternative embodiment, the means for preventing the interfacefrom an exposure to an external electric field form a part of anarrangement for shielding an electronic circuit of the electronic devicefrom external radiation. This has the advantage that the optical devicecan be protected from the build-up of electrostatic charge by extendingan arrangement already present in the electronic device, which iscost-effective.

The invention is described in more detail and by way of non-limitingexamples with reference to the accompanying drawings, wherein:

FIG. 1 schematically depicts a prior art variable focus lens;

FIG. 2 schematically depicts an optical device according to the presentinvention;

FIG. 3 schematically depicts another optical device according to thepresent invention;

FIG. 4 schematically depicts an electronic device according to thepresent invention; and

FIG. 5 schematically depicts another electronic device according to thepresent invention.

It should be understood that the Figures are merely schematic and arenot drawn to scale. It should also be understood that the same referencenumerals are used throughout the Figures to indicate the same or similarparts.

In FIG. 1, a variable focus lens as disclosed in International Patentapplication WO 03/069380 is shown. The variable focus lens comprises afirst fluid A and a second fluid B housed in a cylindrical chamber. Thefluids are immiscible, have different refractive indices and preferablyhave the same density to avoid orientation-dependent gravitationaleffects on the orientation of the fluids including the interface 14between the fluids. The cylindrical chamber further comprises a firstend portion 4 and a second end portion 6, with the first end portion 4as well as the inner walls of the cylindrical chamber being covered by ahydrophobic coating such as AF1600™ from the DuPont company, which maybe combined with a stack of parylene, to confine the conductive fluid Bby the insulating fluid A in the absence of an applied voltage. Theshape of the interface 14 can be switched in a continuous fashion from aconvex shape shown in orientation (a) to a concave shape shown inorientation (b) by varying a direct or alternating voltage from a valueV1 to a value V2 across the cylindrical electrode 2 embedded in thechamber wall and a, preferably transparent, annular electrode 12 on thesecond lid 6 which is in conductive contact with the second fluid B.Consequently, the focal point of the light path L through the cylinderis altered.

The transparent end portion 4 may be a glass or polymer lid or anothersuitable transparent material, which may be lens-shaped. The exposure ofthe container of the fluids A and B to an external electrical field orthe rubbing of the transparent end portion 4, e.g., cleaning the endportion with a cloth or accidental rubbing of the end portion 4 bywearing the optical device in a pocket of a garment, can cause theaccumulation of an electrostatic charge on a surface of the containersuch as the transparent end portion 4. This charge can attract theconductive fluid B, thereby disturbing the shape of the interface 14between the fluids A and B, as shown in (c), thus causing a deviation ofthe desired optical behaviour of the lens. Since it can take severalhours or longer for the electrostatic charge to leak away, it will beobvious that this is a highly unwanted effect. It is pointed out that asimilar unwanted effect can occur when the lens is exposed to anexternal electrical field.

It is emphasized that although this undesirable effect is explainedusing the prior art lens from International Patent application WO03/069380 as an example, other liquid-based optical devices such as thediaphragm disclosed in US patent application US2001/0017985 can equallysuffer from this problem.

In FIG. 2 and the following figures, the variable focus lens of FIG. 1will be shown as an embodiment of the optical device of the presentinvention. It is emphasized, however, that the teachings of the presentinvention also apply to other liquid-based optical devices. In FIG. 2,the variable focus lens of FIG. 1 is extended with a conductive layer100 for preventing the interface from an exposure to an externalelectric field of the lens, i.e., on the first end portion 4. Theconductive layer 100 is shown on the inner surface of the end portion 4,but an orientation on the outer surface of the end portion 4 is alsofeasible. The conductive layer 100 can be realized with any knowntransparent conductive material such as indium tin oxide (ITO), Indiumtrioxide (In₂O₃) or tin dioxide (SnO₂). Preferably, the conductive layer100 is kept at the same potential as the liquid responsive to anelectric field B, which can be realized by conductively coupling theconductive layer 100 to the electrode 12 in contact with the liquidresponsive to an electric field B, as shown in FIG. 2.

FIG. 3 shows another embodiment of an optical device of the presentinvention. The variable focus lens of FIG. 1 is placed inside a furthercontainer 120. The further container 120 may be open opposite the endportion 4 and the end portion 6 of the variable focus lens, or may havetransparent sections opposite those end portions. The further container120 may further comprise a metal body, or may further comprise anon-conductive material such as plastic or glass, which may betransparent. In case of the further container 120 comprising such anon-conductive material, the further container 120 further comprises aconductive coating 140, which may be transparent, and which may resideon an inner surface or an outer surface of the further container 120.

Consequently, the further container 120 acts as a Faraday cage aroundthe variable focus lens, thus preventing a build-up of an electrostaticcharge on a surface of the container. Furthermore, since an externalelectrical field can also disrupt the intended optical behaviour of theoptical device, the Faraday cage also protects the optical deviceagainst such disruptions. The conductive coating 140 may also be appliedto the outer surface of the container of the variable focus lens, inwhich case the further container 120 can be omitted. Preferably, theconductive coating 140 or a conductive further container 120 areconductively coupled to the liquid responsive to an electric field B toensure that the Faraday cage is kept at the same potential as the liquidresponsive to an electric field B. This conductive coupling may berealized via the electrode 12. It is emphasized that the aforementionedembodiments of a Faraday cage may be combined with any of theembodiments of the conductive layer 100 as shown in FIG. 2 withoutdeparting from the scope of the present invention.

At this point, it is emphasized that although in this application themeans for controlling the orientation of the interface 14 are depictedas an electrode arrangement for controlling the shape of the interface14 by means of a voltage, other means for controlling the orientation ofthe interface 14 are equally acceptable, such as the means forcontrolling the orientation of the interface 14 as described inunpublished European patent application 03101335.2 with priority dateMay 14, 2003.

In this application, a variable focus lens is disclosed including twoimmiscible liquids with different refractive indices. The lens has twochambers over which the two liquids are distributed: a first chamber inwhich the interface is positioned and through which the light path runs,and a second chamber having two connections to the first chamber. Thesecond chamber includes a pump, which is used to alter the respectivevolumes of the liquids in both chambers. Consequently, the focus of thelens is varied by a translation of the position of the interface betweenthe two liquids with respect to the inner wall of the first chamberrather than by changing the shape, i.e., the curvature of the interface.

FIG. 4 shows an embodiment of an electronic device 1 of the presentinvention, including an optical device having a conductive layer 100 onthe end portion 4, as shown in FIG. 2 and its detailed description. Theelectronic device 1 further includes driver circuitry 20 for applying avoltage across the electrode arrangement including electrodes 2 and 12,and an image sensor 30 for capturing an image that enters the electronicdevice 1 via the light path of the optical device. The driver circuitry20 and the image sensor 30 are powered by a power supply 40, which hasone of its terminals, e.g., ground, coupled to the conductive layer 100.This may also be the ground of the electronic device 1. Alternatively,the conductive layer 100 may also be coupled to the power supply 40 viathe electrode 12, in an arrangement analogous to that shown in FIG. 2.

FIG. 5 shows another embodiment of an electronic device 1 of the presentinvention, including a liquid-based optical device, e.g., a variablefocus lens, driver circuitry 20, an image sensor 30 and a power supply(not shown). The electronic device 1 further comprises an electroniccircuit 50, which is shielded from external radiation, i.e., radiationfrom outside the electronic circuit, by shielding material 60. Theshielding material 60 may be any suitable material known to the skilledperson, e.g., a conductive foil or a metal housing. The shieldingmaterial 60 is extended over the container of the optical device withoutblocking the light path through the optical device to prevent a build-upof an electrostatic charge on a surface of the container of the opticaldevice.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements. In the device claim enumerating several means,several of these means can be embodied by one and the same item ofhardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. An optical device comprising: a container enclosing an insulatingliquid (A) and a liquid responsive to an electric field (B), theinsulating liquid (A) and the liquid responsive to an electric field (B)being immiscible and being in contact with each other via an interface(14), at least one of the liquids (A; B) being at least partially placedin a light path through the container; means for controlling anorientation of the interface (14); and means (100, 120, 140) forpreventing the interface from an exposure to an external electric field.2. An optical device as claimed in claim 1, wherein the means forcontrolling an orientation of the interface comprise an electrodearrangement (2; 12) for controlling the shape of the interface (14) bymeans of a voltage.
 3. An optical device as claimed in claim 1, whereinthe surface is a part of a transparent end portion (4) of the container;the means for preventing the interface from an exposure to an externalelectric field comprise a conductive layer (100), the conductive layer(100) forming a part of the transparent end portion (4).
 4. An opticaldevice as claimed in claim 3, wherein the means for controlling theorientation of the interface comprise an electrode (12) in contact withthe liquid responsive to an electric field (B), the conductive layer(100) being conductively coupled to said electrode (12).
 5. An opticaldevice as claimed in claim 1, wherein the means for preventing theinterface from an exposure to an external electric field comprise aFaraday cage (120, 140) surrounding the container.
 6. An optical deviceas claimed in claim 5, wherein the Faraday cage comprises a conductivecoating (140) at least partially covering a further container (120). 7.An optical device as claimed in claim 6, wherein the further container(120) is at least partially transparent.
 8. An electronic device (1)including an optical device comprising: a container enclosing aninsulating liquid (A) and a liquid responsive to an electric field (B),the insulating liquid (A) and the liquid responsive to an electric field(B) being immiscible and being in contact with each other via aninterface (14), at least one of the liquids (A; B) being at leastpartially placed in a light path through the container; means (2; 12)for controlling an orientation of the interface (14); and means (60,100) for preventing the interface from an exposure to an externalelectric field; driver circuitry (20) coupled to the means (2; 12) forcontrolling an orientation of the interface (14); and a power supply(30) for powering the driver circuitry (20).
 9. An electronic device (1)as claimed in claim 7, wherein the means (100) for preventing theinterface from an exposure to an external electric field are coupled toa terminal of the power supply (30).
 10. An electronic device (1) asclaimed in claim 8, wherein said terminal is the ground.
 11. Anelectronic device (1) as claimed in claim 8, wherein the means forpreventing the interface from an exposure to an external electric fieldform a part of an arrangement (60) for shielding an electronic circuit(50) of the electronic device (1) from external radiation.